net: fix socket ioctl() bypassing Linux adjustments

Prior to 65ccda4c7b15909e (net: use a file derived class for sockets
 (socket_file)), ioctl()s for socket were directed to linux_ioctl_socket()
and thence to soo_ioctl().  However that commit short-circuited
linux_ioctl_socket() out and dipatched directly to what was previously
known as soo_ioctl() (and became socket_file::ioctl()).  The caused
interface enumeration ioctl()s to fail, for example in Cassandra.

Fix by bringing back the previous behaviour.

Signed-off-by: Avi Kivity <avi@cloudius-systems.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>